The TorPark browser, based on Portable Firefox and small enough to fit on your thumb drive, doesn't leave a trace of your web browsing session behind. In addition to Adblock, TorPark has the Tor network connection capability built in, so you can switch to the anonymous network with the click of a button.

TorPark's been out for some time now, but the developer says the new version is:

...significantly improved, upgraded, more robust. I work on it every weekend. It is cleaner, faster, more integrated, and much much much more robust and fault tolerant. Lots of bugs corrected and new features added. It is definitely not the same program I started a year ago.

In practice the Tor network is super-slow, but you can switch to your regular network easily in TorPark, a must-have USB key addition for anyone concerned about keeping their surfing private. TorPark is a free download, Windows only. — Gina Trapani